Georgia10 reminds us that in a non-Plame related Fitzgerald case he tried to obtained the phone records of some reporters. The judge in that case refused to do so, based on his view of reporters' qualified constitutional source privilege.
So, if the administration is truly going after the phone records of reporters they're unlikely to be doing so using a warrant, or even bothering with a normal Justice Department criminal investigation. They're simply using their powers to get them.